In the operation of blast furnaces and also of shaft furnaces for direct reduction, of boilers, as for example in coal gasification, of crucible furnaces or of low shaft furnaces for melting ferro-alloys, non-ferrous metals or non-metals, a tap hole must be opened after a certain period of time so that the melt or the by-products such as slag can run off. Depending on the process and the melting times, the length of the tapping cycle is between half an hour and several days. After tapping, the tapholes are again closed.
For alternate closing and opening of the tapholes of blast furnaces it is known from EP-OS-No. 41 942, to drive a rod, some minutes after the plugging of the taphole, through the as yet not fully hardened body of plugging material by means of a pneumatic hammer until the tip of the rod reaches the interior of the blast furnace, i.e. the melt.
While the part of the tip of the rod that comes into contact with the molten metal melts away, the remaining part of the tapping rod remains in the plug and is only withdrawn again on tapping.
It is known to use a taphole drilling machine to withdraw the tapping rod. Such machines are standard drilling machines having a striking hammer for driving in the tapping rod. However, to withdraw the tapping rod these taphole drilling machines must be equipped with a second hammer that strikes in the opposite direction to the hammer used for driving in. In addition a remotely controlled gripping device is required to grasp the tapping rod without an operator having to step into the tapping spout or channel for the crude iron. The gripping means and the hammer for driving in and withdrawing the tapping rods together form a compact device whose necessarily space-saving construction makes it very costly and also liable to break down.
To avoid the need for a two-hammer compact device, it has been proposed in EP-OS-No. 122 844 to withdraw the tapping rod from the taphole passage by means of the taphole plugging machine. However, since when withdrawing the tapping rod such machines complete their normal swinging movement, i.e. move in an arc of a circle from their working position at the taphole to a rest position, the rod cannot move in a straight line. The tapping rod is therefore always withdrawn from the taphole at an angle, which results in damage to the taphole and/or the tapping passage.
From U.S. Pat. No. 4 384 706 it is known to burn up the tapping rod with an oxygen lance instead of withdrawing it. However this process takes too long and is accompanied by considerable annoyance caused by smoke.